Re: tx_time tag accuraccy

Marcus! Thanks for you comment.

I think that USRP transmit FIFO is at the start of the DSP chain in FPGA
i.e it is prior to both of the interpolation filters? right? I am not
talking about when the burst will be over the air, I want to know when
the
first sample of the burst will leave the transmit FIFO if it has been
tagged as tx_time=X.


Bob


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Sorry for not stating the hardware earlier. I am using USRP N210, with
RFX2400 and WBX boards.


Bob

On Wed, Jun 4, 2014 at 2:01 PM, bob wole [email protected] wrote:

I think that USRP transmit FIFO is at the start of the DSP chain in FPGA i.e
it is prior to both of the interpolation filters? right? I am not talking
about when the burst will be over the air, I want to know when the first
sample of the burst will leave the transmit FIFO if it has been tagged as
tx_time=X.

If you tag a burst with time X, that burst will be released from the
device buffer at time X - assuming the burst arrives at the device
before time X. After time X, there will be a sample rate dependent
delay and a fixed analog group delay before the burst can be observed
at the antenna output.

In other words, a burst tagged to transmit at time X will leave the
buffer at time X.

-TT

Hi Tom,

Thanks for your comment. I do not think if I tag a burst with time X,
it’ll
go out of USRP transmit FIFO at exactly X, there would be some small
delta
involved depending on the clock resolution, and I want to know that
delta.
I know that there would be some DSP delays, depending on sample rate,
and
analog delays AFTER the burst leave transmit buffer.


Bob

On Mon, Jun 9, 2014 at 2:15 AM, bob wole [email protected] wrote:

Thanks for your comment. I do not think if I tag a burst with time X, it’ll
go out of USRP transmit FIFO at exactly X, there would be some small delta
involved depending on the clock resolution, and I want to know that delta. I
know that there would be some DSP delays, depending on sample rate, and
analog delays AFTER the burst leave transmit buffer.

The N210 clocking rate is 100 MHz, which gives timing resolution of
10ns.

-TT

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